The first leadership election in the history of the SDLP — a battle between deputy leader Alasdair McDonnell and the party’s only Executive minister Margaret Ritchie — gets under way tonight.

Until now SDLP leaders have been anointed rather than appointed — founder Gerry Fitt giving way to John Hume and, for the last nine years, Mark Durkan — and now the party appears sharply divided over a successor.

By some reckonings Social |Development Minister Ritchie appears to be narrowly ahead of South Belfast MP McDonnell, but the contest is too close to call.

And a narrow victory for either come Sunday could leave a bruised and divided party, unable to rally round the new leader. Unsurprisingly, both the McDonnell and Ritchie camps claim victory is within grasp. Sixty-year-old McDonnell is said to have the backing of two-thirds of the party’s councillors and have a potential winning margin of 40 to 50 votes.

But Ritchie (51) appears to enjoy the support of most of the party’s MLAs and officials and sectors like the youth wing.

Voting opens when the conference does, at 7pm tonight, and closes at 6pm tomorrow night.

A total of 414 delegates are entitled to vote and of those whose intentions are declared — the party’s Assembly group, its 98 councillors, party officers and its youth group — Ritchie is comfortably ahead. But there are some 200 ‘unknowns’ and McDonnell is perceived to have sewn up those.

Branches are allowed to divide both ways, with individual delegates reflecting the split. A branch with 10 delegates where support divided 60/ 40 would in theory vote six for one and four for the other.

But the fact that it is a secret ballot, and that branches will have had to find individuals willing to vote against their own preference in certain cases, means the branch break-down may not be accurately reflected in the final votes.

Mid-Ulster MLA Patsy McGlone might have been expected to sew up that branch for McDonnell, but Ritchie is said to have made inroads. Conversely, the party’s largest branch, Balmoral in South Belfast, with 16 delegates, was expected to support Ritchie but McDonnell is understood to be guaranteed at least three votes there.

And key individuals also have a role to play. Mr Hume and his wife Pat are due to arrive at the gathering, in the Slieve Donard Hotel in Newcastle, this afternoon and are said to be siding with Ritchie. Mrs Hume yesterday declined to reveal which candidate she is supporting but confirmed that, because she is not a delegate, she will not actually have a vote.

Mr McGlone will also be declared the new deputy leader. He is unopposed.